1. Field of the Invention
The present invention relates to a corneal punch for cutting corneal grafts from donor corneas prior to transplantation of the grafts to patients with damaged or diseased corneas.
2. General Background of the Invention
In the field of eye surgery, it is sometimes necessary to perform a corneal transplant by replacing a diseased or damaged cornea of a patient with a donor cornea harvested from an immunologically compatible cadaver. This is generally achieved by removing at least a central portion of the diseased or damaged cornea from a patient's eye using a trephine, using a corneal punch to cut an equivalent portion from a donor cornea (this portion being known in the art as a donor graft), and then inserting the donor graft into the space on the surface of the patient's eye left vacant by removal of the diseased or damaged portion of the patient's original cornea.
A known corneal punch comprises a base unit including a well in which a donor cornea may be located, and a guide unit which is then placed on top of the base unit and registered therewith by way of four pins provided on the underside of the guide unit and which locate into four corresponding holes provided on an upper peripheral surface of the base unit. The guide unit is a generally solid block of similar size to the base unit, and includes a central aperture which is located directly over the well of the base unit when the guide unit is in registration therewith. The central aperture is circular, and is sized and shaped so as slidably to receive a corneal trephine. The corneal trephine may be moved up and down within the guide unit in a reciprocating manner so as to allow a donor graft to be cleanly cut from the donor cornea.
This known corneal punch has two significant disadvantages. Firstly, it is difficult to register the guide unit with the base unit because the four pins are difficult to locate within the four holes. Secondly, because the guide unit is substantially solid and opaque, it is not possible for a surgeon or technician to have a clear view of the donor cornea when cutting the donor graft therefrom with a corneal trephine.
According to the present invention, there is provided a corneal punch comprising a base unit having a first annular mating surface surrounding a well in which a donor cornea may be located, and a separate guide unit including an inner annular guide shaft and an outer locating ring connected to the guide shaft and having a second annular mating surface, wherein the base unit and the guide unit may be releasably positioned in registration with each other by way of the first and second mating surfaces such that the guide shaft is substantially coaxial with the well.
Advantageously, the outer locating ring of the guide unit is connected to the guide shaft by way of one or more spokes or webs so as to provide one or more windows in the guide unit. The one or more windows allow the well to be observed when the guide unit is in registration with the base unit. Furthermore, a donor cornea or donor graft may be manipulated through the one or more windows when in the well, for example with a pointed tool or the like, for positioning or other purposes.
The one or more spokes or webs may be provided with corrugations or ridges or the like on upper surfaces thereof so as to provide a good gripping surface for a person's fingers when pushing down on the guide unit so as to ensure it is held firmly in place on the base unit when the corneal punch is in an assembled condition. Alternatively or in addition, the inner annular guide shaft of the guide unit may be provided with peripheral ridges or corrugations, such as a knurled outer edge, for providing a finger grip.
Alternatively, the guide unit or at least a part thereof, preferably a part between the locating ring and the guide shaft, may be made out of a substantially transparent material so as to allow the well to be observed when the guide unit is in registration with the base unit.
In this way, the present invention provides a corneal punch where it is relatively easy to position the guide unit in registration with the base unit, in which the well is visible to a surgeon or technician when the guide unit is in place, and in which access to a donor cornea or donor graft is provided through one or more windows so as to allow the cornea or graft to be manipulated or repositioned when in the well.
The first and second mating surfaces may comprise annular mating flanges and shoulders so as to provide good registration between the base unit and guide unit. The annular mating flange of the first mating surface may fit inside the annular mating flange of the second surface, or vice versa.
The guide shaft is sized and shaped so as slidably and snugly to receive an annular corneal trephine, and to allow a cutting edge of the trephine to be lowered into the well so as to cut a donor graft from a donor cornea located therein.
The base unit may be provided with peripheral finger grips or the like so as to allow it to be held firmly in position on a flat surface when cutting a donor graft from a donor cornea. The finger grips may take the form of corrugations or ridges or the like formed on a surface of the base unit. In some embodiments, the base unit includes a generally planar base plate which allows the corneal punch to be held down on a flat surface in a secure manner. The base plate may include a generally annular cut-out portion in which a corneal trephine may be snugly located for storage purposes.
In preferred embodiments, the present invention is made out of surgical grade stainless steel, although other materials such as plastics or polymers or other metals may be used where appropriate. The guide unit in particular may be made fully or partially out of a substantially transparent plastics material so as to allow the well in the base unit to be observed when the guide unit is in position.
It is preferred that the present invention is a disposable corneal punch, in that it is discarded after use. However, certain embodiments may be sterilised, for example in an autoclave, and then used again.
The well may comprise a generally circular concave dish sunk into a central part of the base unit and adapted to contain a donor cornea.